A. Related Applications
There are no applications for patent relating hereto heretofore filed in this or any foreign county.
B. Field of Invention
Our invention relates generally to a sticker positioning apparatus and more particularly to such apparatus that precisely positions stickers onto a lumber stack immediately therebeneath.
C. Description of the Prior Art
Lumber is cut at geographically convenient sawmills from fresh cut or so called "green" logs that have been stockpiled in yards at the sawmills. Such logs may remain outdoors for extended periods of time awaiting processing and, due to their cellular makeup, do not dry to thereby require rough lumber cut from them to be dried prior to finishing and sale to minimize warpage. Green lumber in the industry is stacked in tiered arrays for subsequent air or kiln drying. To enhance the drying procedure, spacers, or "stickers" as they are known in the industry, are positioned between successive horizontal tiers to permit circulation of drying air between the tiers of freshly cut lumber. The so arranged stacks of lumber thereby present both faces of green lumber to effectively utilize drying air.
It is important in the stacking of lumber in layers for drying to have stickers be not only horizontally spaced in a predetermined array, but also that the stickers separating the tiers themselves be in substantial vertical alignment to one another. This alignment is important, firstly because it limits shear forces from being imposed on the respective layers of freshly cut lumber and thereby inhibits breaking of boards or stretching of fibers and cracking with attendant economic losses. Secondly, it enables lumber to dry without warpage induced by stickers that are vertically offset from one another. Green lumber is of a somewhat semi-plastic nature such that if any concentrated force be applied at an area of limited extent, the lumber or its fibers will permanently move to warp or take on a "set" as the condition is commonly called. This is especially true of green lumber at an elevated temperature or with a high moisture content as in a steam kiln. Warping, if it occurs, brings about substantial loss of useful boards as warped lumber is of very limited economic value.
Proper automated positioning of stickers has heretofore eluded the industry. One of the more common and fairly effective past practices to position stickers has been by manual labor, but escalating costs of labor has lowered the competitive value of this practice, so mechanical means have been sought to provide proper sticker positioning. Unfortunately the mechanical sticker positioners of the past have lacked ability to maintain stickers in a predetermined vertical array to avoid problems as noted above, have not been economically feasible, have not had required durability and reliability or have not been operative with existing stackers.
Automated sticker placement mechanisms in the past have generally positioned stickers above a lumber course merely by dropping stickers upon a lumber stack by gravity. Accordingly, the desired optimum sticker position, with vertically adjacent stickers in stacked array, is only randomly achieved as stickers tend to rebound and move after impact with a lumber stack, and may not be properly positioned in the first instance. This repositioning effect is lessened to an extent by lumber stackers that have utilized known elevator means to vertically reposition the lumber stack with each successive array positioned thereon. In this manner the height from which the stickers are dropped is lessened to lessen the randomness of their positioning. Manual labor also has been employed to assist in correctly positioning stickers on the stacking lumber to maintain their alignment, but with commensurate increases in costs of operation.
Our invention seeks to alleviate these problems, especially in an elevator-type stacking mechanism that maintains the top of a lumber stack at a predetermined vertical position. In so doing our invention residues not in any single element set forth, but rather in the synergistic combination of all of its individual structures that necessarily result in the functions flowing therefrom.